Look up a couple of weather stations near you on Wunderground.
Down near the bottom of the current graphs (Temp, pressure, wind) ,
some have Solar Radiation W/sq M (orange) recorded.
Look not only on how much, but how long (the area under the curve) , that is what will be available to charge your device.
The numbers in the Ads are for
clear, sunny days at optimum angle(and those might be for only an hour in your area depending on SEASON).
OH! Most dedicated readers take 5VDC (The older USB A/B. micro/mini), Most roof (the big ones) solar panels are 12V
individually and have controllers to regulate/Invert to AC.
Unless you need AC for other reasons, avoid those 'solar generators' (besides, they ain't light). Every conversion wastes some energy doing the conversion.
If your device takes USBC (directly), It may support 'turbo mode charging'. Having your solar
support that mode might be a plus (it will charge on regular USB 5V if mode not available or the device will not accept)
Also don't sucker in on a lot of Internet ads.
Your device controls the maximum charge it will ACCEPT. The power source is a LIMITING factor
only if the device can ask for more current.